On a Raspberry Pi (Debian Buster) I use this for Serial Gadget (based on phk's answer):

sudo nano .profile

add:

# resize function for connected serial console
resize() {
  old=$(stty -g)
  stty raw -echo min 0 time 5

  printf '\0337\033[r\033[999;999H\033[6n\0338' > /dev/tty
  IFS='[;R' read -r _ rows cols _ < /dev/tty

  stty "$old"

  #echo "cols:$cols"
  #echo "rows:$rows"
  stty cols "$cols" rows "$rows"
}

ALL_COMMANDS_FINISHED=1

PreCommands() {
  if [ "$ALL_COMMANDS_FINISHED" = '1' ]; then
    ALL_COMMANDS_FINISHED=0
    resize
    #echo "1->0"
  fi
}

PostCommands() {
  ALL_COMMANDS_FINISHED=1
}
  
# if login thru ttyGS0
if [ $(tty) = '/dev/ttyGS0' ]; then
  # PreCommands is called before every single command on a command line
  trap PreCommands DEBUG
  # PostCommands is called after all commands on a command line are finished
  PROMPT_COMMAND="PostCommands"
fi

I use this for Serial Gadget (based on phk's answer).
Calling resize only once per line.

sudo nano .profile

add:

# resize function for connected serial console
resize() {
  old=$(stty -g)
  stty raw -echo min 0 time 5

  printf '\0337\033[r\033[999;999H\033[6n\0338' > /dev/tty
  IFS='[;R' read -r _ rows cols _ < /dev/tty

  stty "$old"

  #echo "cols:$cols"
  #echo "rows:$rows"
  stty cols "$cols" rows "$rows"
}

ALL_COMMANDS_FINISHED=1

PreCommands() {
  if [ "$ALL_COMMANDS_FINISHED" = '1' ]; then
    ALL_COMMANDS_FINISHED=0
    resize
    #echo "1->0"
  fi
}

PostCommands() {
  ALL_COMMANDS_FINISHED=1
}
  
# if login thru tty*
if [ $(tty) = /dev/tty* ]; then
  # PreCommands is called before every single command on a command line
  trap PreCommands DEBUG
  # PostCommands is called after all commands on a command line are finished
  PROMPT_COMMAND="PostCommands"
fi

On a Raspberry Pi (Debian Buster) I use this for Serial Gadget (based on phk's answer):

sudo nano .profile

add:

# resize function for connected serial console
resize() {
  old=$(stty -g)
  stty raw -echo min 0 time 5

  printf '\0337\033[r\033[999;999H\033[6n\0338' > /dev/tty
  IFS='[;R' read -r _ rows cols _ < /dev/tty

  stty "$old"

  #echo "cols:$cols"
  #echo "rows:$rows"
  stty cols "$cols" rows "$rows"
}

ALL_COMMANDS_FINISHED=1

PreCommands() {
  if [ "$ALL_COMMANDS_FINISHED" = '1' ]; then
    ALL_COMMANDS_FINISHED=0
    resize
    #echo "1->0"
  fi
}

PostCommands() {
  ALL_COMMANDS_FINISHED=1
}

# if login thru ttyGS0
if [ $(tty) = '/dev/ttyGS0' ]; then
  # PreCommands is called before every single command on a command line
  trap PreCommands DEBUG
  # PostCommands is called after all commands on a command line are finished
  PROMPT_COMMAND="PostCommands"
fi

On a Raspberry Pi (Debian Buster) I use this for Serial Gadget (based on phk's answer):

sudo nano .profile

add:

# resize function for connected serial console
resize() {
  old=$(stty -g)
  stty raw -echo min 0 time 5

  printf '\0337\033[r\033[999;999H\033[6n\0338' > /dev/tty
  IFS='[;R' read -r _ rows cols _ < /dev/tty

  stty "$old"

  #echo "cols:$cols"
  #echo "rows:$rows"
  stty cols "$cols" rows "$rows"
}

ALL_COMMANDS_FINISHED=1

PreCommands() {
  if [ "$ALL_COMMANDS_FINISHED" = '1' ]; then
    ALL_COMMANDS_FINISHED=0
    resize
    #echo "1->0"
  fi
}

PostCommands() {
  ALL_COMMANDS_FINISHED=1
}
  
# if login thru ttyGS0
if [ $(tty) = '/dev/ttyGS0' ]; then
  # PreCommands is called before every single command on a command line
  trap PreCommands DEBUG
  # PostCommands is called after all commands on a command line are finished
  PROMPT_COMMAND="PostCommands"
fi